Method of frequency or phase modulation



April 5, 1.938. D. G. c. LUCK 2,113,214

METHOD OF FREQUENCY 0R PHASE MODULATION Filed oct. 29, 195e s sheets-sheet 1 April 5, 193s. D, G, C, LUCK 2,113,214

METHOD OF FREQUENCY OR PHSE MODULATION Filed oct. 29, 193s 5 sheets-sheet 2 Clttorneg y nventor *alaaf April 5, 1938. n D. G. c. LUCK 2,113,214

- l METHOD oF FREQUENCY 0E PHASE MODULATION Filed Oct. 29; 1936 y '3 Sheets-Sheet 3 Snventot Gttorneg .hada6.65m@v l.

Patented Apr. 5, 1938 l I l v UNITED'STATES PATENT OFFICE METHOD F FREQUENCY 0B PHASE MODULATION Davia G. c. Luck. maden Heights, N. J., assignor to Radio Corporation of America, a corporation o! Delaware Application October 29, 1936, Serial No. 108,163

18 Claims. (01.2504) My invention relates to the transmission and sexies of modulated impulses for the keying of a reception of energy at radio frequency. lIn parcarrier frequency crrent. ticular, my invention relates to a method of mod- Another object is to provide means for reconulating a carrier by rst creating a phase moduverting said impulsed keyed carrier current into lated Wave which in turn creates a series of moda phase modulated current and for demodulat- 5 ulated impulses which key a transmitter, and to ingsaid phase modulated current. a method for receiving and translating said mod- An additional object is to provide means for ulated carrier. The present application is a conoperating a system of radio communication which tinuation in part of my Patent No. 2,086,918, shows an improved ratio of signal-to-static over dated July 13, 1937, and! assigned to the same conventional systems employing similar amounts 10 assignee as the present application. of power.

For faithful reproduction at the receiver of Fig. irepresents inschematic outline, one emthe modulated signals at the transmitter, it has bodiment of my invention applied to a transmisheretofore been considered essential. that all the sion system,

l5 circuit elements should be linear;V that is. that Figs. 2 and 3 are schematic illustrations of re- 15 they should respond in proportion to the in-` ceiving systemsfor receiving and demodulating tensity of the applied signal. Under this limitathe impulse modulated signals transmitted inactation it has heen known for a number of years cordance with my invention. that any discrimination between desired signal Fig. 4 is val circuit diagram of a carrier fre- 29 and noise entering the signaling system must be quency generator, f

the result of selectivity of the circuits involved. Fig. 5 is a circuit dia of a phase modula-` lf the signal occupies the minimum frequency tor, e range necessary for transmission of the desired -rFig. 6 is a circuit diagram of an impulse genintelligence and the selectivity of the circuit used erator, Y

is such that it passes this signal frequency range Fig'. 'I is a circuit diagram voi an impulse re- 25 freely but suppresses disturbances of all other lay,

frequencies, no further improvement in the ratio Fig. 8 is acircuit diagram of a radio transmitof signal to random noise can be hoped for, exter suitably arranged ior keying,

cept, of course, by increasing the intensity of the Fig. 9 is a circuit diagram of a differentiator transmitted signal. and rectiilers, 30

rl'he possibilities of improvement of the ratio Fig. l0 is a circuit diagram of an apparatus of signal intensity to noise intensity I have found for reconstructing the dots from impulses,

to lie in a departure from ordinary methods of Fig. 11 is a circuit diagram of a lter, and

Vamplitude modulation. I have found also that Fig. 12 is a circuit diagram of a phase demodu- I these possibilities may be extended bythe use of lator. 35

non-linear circuits .having an output -by no lf the amplitude of 4an oscillatory current is means proportional to the input. varied in accordance with a desired signal, the

Briefly, my system contemplates the transmisoscillation is said to be amplitude modulated. sion of certain timing marks. The transmission Likewise, ifthe frequency of an oscillatory cur- 4o of intelligences may be had without in the least rent is varied in accordance with the signal to 40 depending upon amplitude modulation of the be transmitted, the oscillation is said to be frecarrier. The improvement in the ratio of signal uuency modulated. The rate of change of the intensity to noise intensity, therefore, is obtained phase of an oscillatory current is termed the Y largely by virtue of' the fact that these timing frequency of that current. Therefore, it may be marks can be shifted over a wide range by the seen that airequency modulated current may be 45 desired signal, but only over a denite narrow termeda phase modulated current. The diiferrange by any noise of' less amplitude'than the ence between the two depends upon the Particusignal. While any interference causing noise of lar relation between the variations of the origigreater amplitude than the signal is not supnal signal and the variation of phase or frepressed in the operation of my system, it will be quency producedby it The System I am about 50 apparent that the signal-to-noise ratioisinlarge to describe may be adapted to eitherl phase or part improved over what is possible when usingA frequency modulation. p `the generally accepted present-day methods.` Signal frequency currents are phase or fre- An object ci my invention is to provide means quency modulated. The phase or frequency` for converting s phase modulated wave into a modulated currents are converted into a series 5s of variably timed impulses which operate animpulse relay; concurrently a sinusoidal current is converted into a series of uniformly spaced impulses which also operate the impulse relay. 'I'his relay is arranged to be selectively operated to the on condition by impulses of the varlably spaced series and to the off condition by alternately occurring impulses of the uniformly spaced references series. 'I'he output of the relay is used to key a carrier current generator which transmits a series of dots, whose duration is a function of the signal frequency currents.

The condition for a dot, of the character described in my Patent No. .2,086,918, dated July 13, 1937, to end is:

d f()=n (l) where tis time of ending of nth dot, T is dot repe-v tition period.

which is depth of modulation (less than 1) and f(t) is modulating wave (maximum value l).

A phase modulated wave, of unmodulated frequency- ',7. may be defined as A =A., sin [2%)f(f)]=no sin a (2) where B is the maximum phase shift in degrees produced by the modulating signal, which varies with time in accordance with the function of f(t). The phase modulated wave passes through the zero value in one particular direction whenever the angle (which is the phase of the wave) has a value of any integral multiple of 2r radians. Therefore, the times when the phase modulated wave is zero are given by t B r-"sK-n where n is any integer.

Comparison of Equations (1) and (3) shows clearly that the instants at which a set of modulateddots stop are the same as those at which the phase modulated sine wave passes through zero. The foregoingtheory, taken in conjunction withthe explanation of Fig. 1, makes it clear how the passage through zero of a phase modulated wave and a synchronous unmodulated Wave may be used respectively to control stopping tand starting instants of a normal modulated dot rain.

When the modulator is inactive, both groups of impulses are equally and uniformly spaced and the impulses of each group are centrally interspersed between those of the other. modulation is applied, one group of impulses becomes variably spaced, while the other group remains uniformly spaced. Modulation causes the impulses of one group to be varied in-spacing within the limits set by the adjacent impulses of the uniformly spaced group.

In Fig. 1, an embodiment of my invention is applied to a transmitter which comprises a signal source or microphone I whose output circuit is connected to the input of an amplifier 3. The amplifier output circuit is connected to a phase modulator 5. The phase modulator output is connected to an impulse generator 1. A constant frequency generator 3 is connectedto the phase When Y modulator 5 and to a second impulse generator I I.

The output circuits of the impulse generators 1, II are connected to the input of an impulse relay I3. The output of the relay I3 is connected to a keying circuit of a radio transmitter I5. The transmitter is coupled toan antenna I1.

'Ihe operation of the transmitter is as follows: The amplified signal frequency currents I9 are impressed on the phase modulator to vary the phase of the carrier frequency currents which are impressed on the phase modulator. 'I'he phase modulated currents 2| are converted into impulses 23 which are variably spaced or timed as a function of the phase modulation. These impulses v23 are rectified and the positive impulses impressed on the impulse relay I3. 'Ihe carrier frequency currents 25 are also impressed on a second impulse generator to forma uniformly spaced or timed series of. impulses 21 which are likewise rectified. 'Ihe positive impulses are also impressed on the impulse relay I3, which, operating as just described, establishes output currents 28 which are used to key the transmitter I5. 'Ihe transmitter radiates dot modulated carrier waves 3|.

` Suitable receiving systems are schematically represented in Figs. 2 and 3. Referring to Fig. 2: An antenna 33 is suitably coupled to a radio receiver 35.- I'he output of the receiver is connected to a limiter 31 which' is in turn coupled to a diil'erentiator 39. The output of the differentiator is impressed on a pair of rectiiiers 4I. The rectiiiers are connected to dot reconstructors 43, 45 which are connected, respectively, to filters 41, 49. is impressed on a phase demodulation translator 5I which is connected to a signal indicator, such as a loudspeaker 53 or the like.

The operation of this receiving system is as follows: The incoming dot modulatedcarrier wave 55 is amplified and detected by the receiver 35 which may be tuned to attenuate currents of undesired frequencies. 'I'he amplified and rectified dot modulated carrier 51 is'separated from excessive impulses, caused -by static and the like, by the limiting action of a limiter 31. The limited dots 5,9 are separated into discrete positive and negative impulses 6| by the difierentiator 39. These impulses are rectified by a pair of rectiers so that two groups of positive impulses 63, 65 are derived. One group is made up of variably spaced impulses 63 and the other of uniformly spaced impulses 55. Both groups of impulses are converted into dots or square wave form currents 61, 69. The currents of square wave form are passed through filters which smooth out the wave form into varying currents 1|, 13. One, 1|, of these varying currents is phase or frequency modulated; the other, 13, is sinusoidal. These currents 1|, 13 are impressed on the phase demodulation translator 53 to form a current 15 which represents the original signal and which actua-tes a loudspeaker or other signal indicator to thereby reproduce the signal.

The second receiving system, illustrated by Fig. 3, is comprised of a signal collector 11 which is attached to a receiver 19 comprising a tunable amplier and a detector. The output circuit of the detector is connected to a limiter 8| which is in turn connected to a diflerentiator 83. The output circuit of the diflerentiator is coupled to a rectier 85. 'I'he rectifier 85 is connected to a dot reconstructor 81, whose output circuit is connected to a tuned circuit 83 which is in turn connected to a second rectifier 9|. The output of The output of the filters l1, 48v

i rier currents are impressed on the tuned circuitsv |35, |31 in 90 phase relationship. through suit-v this rectifier 9| includes 'a signal indicating in-` strument93.

The operation of the second receiving system is essentially as followsz' The impulse modulated carrier waves 95 induce currents inthe antenna. which are selectively amplified and detected by the receiver 19. The rectified or detected currents are limited to eliminate excessive static or like impulses. The limited modulation currents 99 are onverted into discrete impulses These impulses are rectified to form a single group of positive im ulses |03 which are variably spaced. -The varia ly spaced impulses |03 actuate a dot reconstructor which converts impulses into currents lwhich have a square wave form |05. By impressing these currents on a circuit 89, which is suitably tuned j ust off resonance, the frequency modulated currents may be converted into amplitude modulated currents, as indicated by reference numeral |01. The amplitude modulated currents |01 are again rectified, and the thus rectied currents |09 impressed on a signal indicating instrument 93, which reproduces signals substantially equivalent to the original signals.

Having described the general method of transmitting and receiving, I shall briey describe some of the component parts. Inasmuch as there are numerous devices which will create the desired eil'ects, it should be understood that the following components are set forth by wayof example rather than limitation.

The microphone and amplifier 3 may be any of the conventional devices well known to those skilled in the art. In Fig. 4 is illustrated a carrier frequency generator which is comprised of a piezo-electric crystal which is connected to the input circuit of a thermionic tube ||3. The output circuit of this tube ||3 includes a tunable circuit ||5 and output circuit terminals ||1.

The phase modulator, represented in Fig. 5, compresas an audio input transformer ||9. The secondary terminals of transformer ||9 are connected to the one set of grid electrodes |20, |22 of thermionic tubes |2|, |23. .The mid-tap of the transformer ||9 is connected through a suitable bias means |25 to the cathodes of the tubes |2|, |23. 'Ihe anode electrodes are connected .together and to a.` resonant circuit |21 which is connected to the anode current source |29. A second set of grid electrodes |3|, |33 are respectively coupledto tuned circuits |35, |31 which are resonant to thev carrier currents. The carable coupling means |39. The second set of grid electrodes |3|, |33- may be biased either positive- -ly or negatively, depending upon Athe type of tubes and the tube characteristics. The output circuit of the phase modulator is represented by an output circuit |4I.v

The impulse generators 1 are each represented by Fig. 6, and are constituted as'follows: A current limiter |43,which may be a pair of suitably biased resistance coupled thermionic tubes |45, |41. The output of the current limiter is applied to a dii'ferentiator comprising aserially connected capacitor |49 and resistor |5|. The input bias voltage of the--flrst tube |45 isa'diusted to normally prevent anode current'from flowing in the anode circuit of the first tube |45. The second tube |41is adjusted to permit'- full anode current to now. As the input voltage across the input terminals of the rst tube is increased, a

potential will be reachedat which anode current will flow in the first tube' |45. The current in the anode resistor of the first tube |45 places a negative grid bias on the second tube |41 which vtends to block currents in the anode circuit 'of the second tube |13. Thus the limitationrisobtained and, as an incident, these tubes |45, |41 may also amplify.

The diierentiator, comprising the capacitor |49 which has .a relatively high reactance with respect to the resistance of the resistor |5|, acts on the output currents of the limiterl |43 to produce discrete, sharply' peaked impulses. The impulses are impressed on the input circuit of a thermionic tube |53 which is biased to cut oi its anode current, thereby making the tube |53 only responsive. to the applied positive impulses. These impulses may be used to directly key a transmitter whereby variably timed and uniformly timed impulses may be sent out, or they may be used to operate an impulse relay.

One form of impulse relay is represented schematically in Fig. 7. The impulse relay employs a pairof thermionic tubes 55, |51 which are connected as a multi-vibrator. The multivibrator is adjustedsothat it has a free frequency of the order of the carrier frequency, and is controlled by impressing the positive impulses, of uniform and variable timing or spacing, on the input circuits. The uniformly spaced impulses are impressed on the input |59 of one,

|55, of the pair of tubes, and the variably spacedimpulses are impressed on the input |6| of the other, |51, of the pair of tubes. The output circuit of the impulse relay is represented by reference numeral |63.

The output circuit of the impulse relay is connected to key a conventional radio transmitter, which is illustrated schematically in Fig. 8. A thermionic oscillator |65 isarranged with a resonant input circuit` |61 and aresonant output circuit |69. The input circuit includes terminals |1|, which are connected to the keying source. The output circuit |69 is suitably coupled to an antenna |13, from which the impulse modulated carrier wave is'radiated.

The receiving-system is comprised of the following units: A signal collecting antenna which is connected to the input of a conventional radio receiver, such as a tuned radio frequency amplier and detector, a superheterodyne or-the like. `Such receivers` require no detailed description, as they are well known to those skilled in the art. The detector output is impressed on a limiter, such as was described in connection. with Fig. 6.

The differentiator circuit 39 for the lreceiving system is somewhat different from the differentiator used in the transmitting system. The present diner'ntiator is shown schematically in Fig. 9, which includes a pair of rectiers. The input circuit |15 includes a resistor 11 and a portion of the inductor |19 which is tapped at a point intermediate its ends. 'I'he tap/is connected through a biasl means |9| to the cathodes of a pair of rectiflers |93, |95. The signal gridsof these tubes are connected, respectively, to the ends of the inductor |19. Thelsc'reen grid electrodes may be biased positively with respect to the cathodes by a connection to the anode current source |81. The. anode electrodes are connected through a pair of resistors |69, |9| to the positive terminal of the anode current source. The output circuit includes connections to each anode and to the junction of the resistors. 'I'he combination of the vdiiferentiator andthe. pair of rectifier-s first converts the currents of square' wave form into discrete positive and negative impulses, corresponding, respectively, to increasing and decreasing limiter output, and then rectiiies these impulses so that the twogroups of positive impulses 53, 65 are derived in the output circuit of the rectiflers.

The two groups of positive impulses are reconstructed into two currents of square wave form by the dot reconstructor apparatus shown in Fig. 10. 'I'hls circuit is characterized by the fact that alternate input impulses start and stop the current ow in the output circuit. This feature has been disclosed and claimed in my copending application entitled Impulse operated relay, Serial No. 47,675, led October 31, 1935. The input circuit |93 is connected to the grid electrode of a gas filled relay tube |95. 'Ihe relay tube is self-biased and protected by a resistor |91. The voltage drop across this resistor |91 is impressed on the input circuit of a thermionic tube |99. A variable capacitor 20| is shunted across the output circuit of the gas filled relay tube. 'I'he anode circuits of both tubes |95, |99

are respectively completed by resistors 203, 205.

The output of the dot reconstructor includes the latter resistor 205 and a blocking capacitor 201.

The pair of dot reconstructors 43, 45 are connected to a wave shaping network which is shown in Fig. l1. The input circuit of the filter is composed of a resonant circuit 209. The output circuit of the filter is composed of a second resonant circuit 2| I.' 'Ihe two resonant circuits are coupled by any suitable type of mutual coupling, such as M. 'The degree of coupling is one of the factors which determine the relation width of the frequency band which the illter will pass. The effect of the iilter is to re-shape a square wave v:form 61, 69 to a sinusoidal wave 1|, 13 (see Fig. 2).

The output of the filters 41, 49 is impressed on` f nected to the junction 22| of the cathode electrodes. l

The second receiving system, shown in Fig. 3, employs component parts which are essentially similar to the first receiving system, with the following modications: A single rectifier 95 and single dot reconstructor 81 are used in place of. the pair of rectifiers 4| and pair of dot reconstructors 43, 45. 'Ihe filters 4 1, 49 may be replaced by a conventional tuned circuit 09 which is comprised of an Inductor and a capacitor. The tuned circuit is adjusted just oi! resonance to convert the frequencymodulated wave into an amplitude modulated wave. The phase modulation translator 5| is replaced by a single rectifier 9| and signal indicator 93.

In the several systems multi-purpose tubes may replace separate tubes. In both receiving systems, the limiters 31, 8| may be eliminated, although I prefer to use limiters for the obvious improvement in signal-to-static ratio. In the foregoing specification I have described the apparatus for and the method of generating a carrier current which is divided into a sinusoidal reference current and a phase modulated current. These currents are' converted into two` groups of discrete impulses, one of which is uniformly spaced and the other is variably spaced. These impulses may be used either to directly key a transmitter, or may be converted into currents of square wave formwhich key the transmitter. The transmitted impulse or dot modulated wave is received and reconverted into phase modulated currents which are translated to reproduce the signal currents. Y

I claim as my invention:

1. In a system of the character described, means for phase modulating a locally generated oscillation by a signal representing current, a local oscillator for generating constant frequency carrier currents, means for converting said phase modulated currents and said carrier frequency currents into two series of positive impulses, and means for transmitting said series of positive impulses. f

2. In a system of the character described, means for phase modulating a locally generated oscillation by a signal representing current, a. local oscillator for generating constant frequency carrier currents, means for converting said phase -modulatd currents and said carrier frequency currents into a series of phase modulated positive impulses, a radio wave transmitter, and a relay controlled by said impulses for keying said transmitter.`

3. The method of transmitting a radio wave which consists in phase modulating a carrier current by a signal representing current, generating a constant frequency carrier current, ap-

plying said modulated and said carrier currents to the input of a generator of positive impulses, applying the so generated impulses to start and stop the flow of a local source of current, and applying such local currents to key a transmitter.

4. The method oi.' transmitting a radio wave which consists in phase modulating a carrier current by a signal representing current, generating a constant frequency carrier current, applying said modulated and said carrier currents to the input of a positive impulse generator, and keying a transmitter with said positive impulses.

5 In a system of the character described, means for generating a constant frequency carrier current, means for phase modulating said current with signal representing currents, means for converting said modulated current and said f carrier current into discrete impulses, means for converting said discrete impulses into currents of square vwave form, and means actuated by said currents of square wave form for keying a transmitter.

6. In a system of the character described,

means for generating a'constant frequency carform for keying a transmitter.

'1. In a system of the character described, means for generating a constant frequency carrier current, meansv for phase modulating said current with signal representing currents, means for converting said modulated current and said carrier current into discrete impulses which are respectively variably spaced and uniformly spaced, and means actuated by said discrete impulses for keying a transmitter.

8. In a system of the character described, means for generating a constant frequency carrier current, means for phase modulating said current with signal representing currents, means for converting said modulated current and said carrier current into discrete impulses, means for converting said discrete impulsesvinto currents of square wave form, means actuated by said currents of square wave form for keying a' transmitter, means for radiating signal waves from the said keyed transmitter, means for receiving said waves, and means for converting said waves into signal representing currents.

9. In a system of the character described, means for generating a constant frequency carrier current, means for phase modulating said:

currentwith signal representing currents, means for converting said modulated current and said carrier current into discrete impulses which are respectively variably spaced and uniformly spaced, means actuated by said discrete impulses for keying a transmitter, means for radiating and means for converting said waves into signal signal waves from the said keyed transmitter,

representing currents.

10. The method of signaling which comprises generating a constant frequency carrier current, modulating a portion of said current by signal currents to form a phase modulated current, converting said phase modulated portion into discrete positive impulses, converting said unmodulated portion of carrier current into discrete positive impulses, and applying said impulses to con differentiating currents derived by said detector,

means for rectii'ying said dierentiated currents to obtain discrete unidirectional impulses, means currents into discernible signals.

15. The method of receiving modulated carrier currents of the 'character described which comprises amplifying and detectingsaid carrier currents, differentiating said currents to form discrete impulses, rectifying said impulses, converting said rectified impulses into currents of square Wave form, Shaping Said- Square Wave form (21.11'-` rents into gradually varying currents, and translating said gradually varying currents into signal representing currents.

-16. The method of receiving modulated carrier currents of the character described which comprises amplifying and detecting said carrier currents, limiting said currents, diiferentiating said currents to form discrete impulses, rectifying said impulses, converting said rectiied impulses4 into currents of square wave form, shaping said square wave form currentsy into gradually varying currents, and translating said gradually varying currents into signal` representing currents.

17. Themethod of receiving modulated carrier currents of the character described which comprises amplifying and detecting said carrier currents, diierentiatlng said currents to form discrete impulses, rectifying said impulses to form groups of uniformly spaced and variably spaced impulses, converting said uniformly spaced impulses and said variably spaced impulses into two separate currents of square wave form, ltering said two currents to obtain gradually varying currents,A and translating said gradually varying currents into signal representing currents.

their detection.

DAVID G. C. LUCK. 

